Purwanto, O. D., Sudradjat, S. and Supijatno, S. (2017) “Determination of Nitrogen Fertilizer Requirement for Four-Year-Old Oil Palm”, Asian Journal of Applied Sciences, 5(6). Available at: https://www.ajouronline.com/index.php/AJAS/article/view/5097 (Accessed: 1December2020).